The Cenozoic (66 million years ago to the present) is the era in which mammals rapidly diversified and humans eventually appeared. Climate change, from gradual cooling to cycles of ice ages, is another major theme of the Cenozoic.
Basic Knowledge
The Cenozoic is divided into three periods: the Paleogene (66–23 million years ago), Neogene (23–2.58 million years ago), and Quaternary (2.58 million years ago to the present). After the K–Pg mass extinction, mammals underwent adaptive radiation and rapidly diversified to fill vacant ecological niches.
Earth has gradually cooled throughout the Cenozoic. The Antarctic ice sheet first formed approximately 34 million years ago, at the Eocene–Oligocene boundary. Beginning approximately 2.58 million years ago, at the start of the Quaternary, Earth entered an age of repeated glacial and interglacial periods, and continental glaciers also developed in the Northern Hemisphere.
Human evolution occurred mainly in Africa. Humans diverged from the common ancestor of humans and chimpanzees approximately 7 million years ago, and Australopithecus (upright bipedal walking) appeared approximately 4 million years ago. Approximately 2 million years ago, Homo erectus (use of fire and expansion outside Africa) appeared. Modern humans (Homo sapiens) originated in Africa approximately 300,000 years ago and spread throughout the world approximately 60,000–70,000 years ago (Out-of-Africa theory).
When did the Quaternary begin, and what climatic characteristics does it have?
Answer: The Quaternary began approximately 2.58 million years ago. It is an age in which glacial periods (cold periods) and interglacial periods (warm periods) alternate, and continental glaciers in the Northern Hemisphere repeatedly developed and retreated. The present is an interglacial period following the last glacial period.
- Three Cenozoic periods: Paleogene → Neogene → Quaternary
- Adaptive radiation of mammals after the K–Pg extinction
- Formation of the Antarctic ice sheet: approximately 34 million years ago (Eocene–Oligocene boundary)
- Beginning of the Quaternary: approximately 2.58 million years ago; start of glacial–interglacial cycles
- Australopithecus: approximately 4 million years ago; upright bipedal walking
- Homo sapiens: originated in Africa approximately 300,000 years ago
- Global expansion: approximately 60,000–70,000 years ago; Out-of-Africa theory
Points to Note
① Although the Cenozoic is called the Age of Mammals, angiosperms, birds, and insects also diversified during this era. ② Do not confuse the Quaternary (2.58 million years ago to the present) with the Cenozoic (66 million years ago to the present). ③ Australopithecus does not belong to the genus Homo; it represents a stage that achieved upright bipedal walking. Do not confuse it with Homo sapiens.
Practice
- State the three Cenozoic periods in order from oldest to youngest.
- When and where did Homo sapiens originate?
- State the characteristic climate changes of the Quaternary.